A variable discharge fuel pump is utilized to maintain a pressurized fuel supply for a plurality of fuel injectors in a common rail fuel system. For example, U.S. Pat. No. 6,311,674 (the '674 patent) to Igashira et al. teaches a fuel pump having a driveshaft and three plungers radially oriented around the driveshaft. As the driveshaft rotates, the plungers reciprocate inward toward the driveshaft to draw fuel past a metering valve and through an inlet port of the pump. As the plungers are displaced away from the driveshaft, fuel is discharged through an outlet port of the pump to a common fuel rail.
The pump of the '674 patent is inlet regulated by controlling movement of the metering valve. Specifically, in response to a desired discharge flow rate of fuel and a desired rail pressure, a current map is referenced to determine a current signal sent to the metering valve. For example, as the desired quantity of fuel delivered to the common fuel rail or the desired fuel pressure within the common fuel rail increases, a higher current level is determined from the current map and a corresponding signal sent to the metering valve to increase the opening area of the metering valve. The increased opening area allows for a greater amount of fuel to be drawn into the pump and subsequently discharged to the common fuel rail.
Although the pump and control strategy of the '674 patent may provide a sufficient flow of pressurized fuel to the common fuel rail, it may be limited, and lack a signal-failure provision. In particular, because the control strategy of the '674 patent utilizes a single current map that is dependent on desired flows and pressures, the control strategy may be applicable only to a particular pump and a particular metering valve. In other words, if either a different pump or metering valve (i.e., a pump with a different displacement or a valve with a different opening area-to-current input relationship) was implemented into a particular application, a completely new control strategy would be required to provide the desired fuel flows. Further, the control strategy of the '674 patent does not provide for the condition when transmission of the current signal to the pump is interrupted.
The disclosed pump control system is directed to overcoming one or more of the problems set forth above.